1. Field of the Invention
The invention relates in general to vehicle anti-theft security systems which operate by controlling when at least one electrically-operated actuator on the vehicle may be operated, and in particular to anti-theft systems for off-road vehicles employing access codes and electrical circuits for recognizing such codes.
2. Discussion
Self-powered vehicles used in the construction and agricultural industries, which often are very expensive, are subject to theft and operation by unauthorized persons, just like conventional highway vehicles, i.e., cars and trucks. Yet, providing adequate security systems to deter theft or unauthorized operation of off-road vehicles poses special problems not normally associated with cars or trucks. Cars and trucks are traditionally designed and built to have lockable operator and engine compartments; deterrents against theft can therefore be achieved through security systems which keep unauthorized persons out of the operator and engine compartments. In contrast, construction vehicles and many agricultural vehicles are often built with operator compartments which are not lockable or otherwise easily secured against unauthorized entry.
Unlike most highway vehicles, which typically are only operated by one or a few individuals over a lengthy period of time, self-powered construction equipment and certain types of agricultural equipment are often operated by many persons, especially when the equipment is frequently moved between work sites. Workers in the construction and agricultural fields are often employed on a short-term basis and tend to change employers frequently, which compounds the difficulty of maintaining vehicle security.
Key-operated ignition switches provided on most off-road vehicles do not by themselves always provide adequate security. Keys can be duplicated or stolen. The locks into which the keys fit can be picked or smashed. Also, a thief can "hot-wire" the vehicle, thus bypassing the ignition key altogether. Hidden "kill" switches wired in series with a normal key-operated ignition switch can also be provided to deter the amateur thief or unauthorized user. The professional thief, however, makes it his business to learn how to locate and defeat kill switches or other such devices or bypass them, along with the normal ignition switch, when hot-wiring a vehicle. Moreover, when many different people operate a vehicle, the location of the hidden device does not remain a well-kept secret. Even repair shop personnel are told how to defeat the security system so that they can test the vehicle after the repairs they are making are complete. Also, such hidden devices cannot be installed as economically by the vehicle manufacturer as original equipment, since the location of the hidden devices must be varied from unit to unit of the same type of vehicle.
The problems mentioned in the foregoing paragraph are also present in cars and trucks. A number of different security systems for cars and trucks have been developed to overcome them as disclosed, for example, in the following U.S. patents:
______________________________________ U.S. Pat. No. Inventor ______________________________________ 3,619,633 Brandon 3,670,836 Tonkowich et al. 3,731,156 Watson 3,756,341 Tonkowich et al. 3,907,060 Burton et al. 4,232,758 Crosas 4,691,801 Mann et al. ______________________________________
The first four patents listed above disclose security systems which have various means for physically protecting control circuitry in an electricallyoperated actuator of a vehicle operated by that circuitry against tampering or being easily bypassed. The techniques disclosed include: (1) placing coding switches, control relays and an ignition coil inside a locked steel box; (2) placing an epoxy-encapsulated circuit and solenoid for a fuel shut-off valve inside a hardened metal casing locked to the vehicle's carburetor; and (3) placing decoding circuitry and a solenoid-operated fuel shut-off valve inside a sturdy weather-proof box.
All of the foregoing patents also disclose security systems which intentionally employ coded signals or access codes to make it more difficult to defeat the disclosed system. In the Brandon patent, the disclosed security system employs two sets of changeable coding switches in a locked box that determine which two of eight pushbuttons on an operator panel on the dashboard must be depressed in order to disarm the security system so that the vehicle may be operated. The security systems disclosed in the two Tonkowich et al. patents, the Watson et al. patent, and the Crosas patent also employ multiple pushbuttons or switches on an operator's panel for entering an access code. In most of the vehicle security systems disclosed in these four patents, the buttons or switches must also be actuated by the vehicle operator in a predetermined sequence. Failure to enter the correct access code and/or sequence results typically in the electrical circuitry of the security system entering a latched-up state so that further attempts to disarm the system cannot be made until power is removed from the system. In the security systems disclosed in the Burton et al. patent and the Mann et al. patent, the coded signals are transmitted by use of radiowave or infrared beam to a receiver located on the vehicle.
One problem with those security systems disclosed in the aforementioned patents which employ circuitry in an enclosure located at the electrically-operated actuator is that a multiple conductor interconnection is required to communicate coded information between the operator's panel and the enclosure. The Tonkowich et al. systems use a special "tamper-proof" cable having multiple dummy conductors and other special features through which a full-voltage electrical signal is sent to energize a solenoid in a hardened casing. However, special cables or wiring harnesses having multiple conductors for passing information between two wellseparated locations on a vehicle add to the cost and tend to reduce the long-term reliability of the electrically-operated security systems. Using fewer conductors to pass such information is therefore desirable.
Another shortcoming of the aforementioned security systems is that each system uses only one access code which cannot be readily changed by the operator or owner of the vehicle. Where there are many operators or other personnel who over time learn the access code for the vehicle, this greatly dilutes the integrity of such vehicle security systems. If the vehicle owner cannot change the code himself, he has no way to protect against the dishonest employee or the suspicious repairman who has leaned the access code. In time, the owner may not even be sure how many people know the code, since some individuals may learn the code through an overheard conversation or breach of security procedures.
Another criterion for evaluating the effectiveness of a vehicle security system is how long it takes the average thief to defeat or bypass it. The longer it takes a thief to defeat a security system, the more likely it is that the thief will abandon his efforts to steal the vehicle or not even bother with attempting to steal it. The longer a thief must work to defeat a security system, the greater is the risk that his unauthorized presence and criminal activity will be detected. Thus, it is desirable to provide a security system which is difficult and time-consuming to defeat or bypass.
However, an anti-theft security system should be easy, not difficult, for an authorized user to disarm, so that the vehicle can be used. The security system should not be prohibitively expensive or significantly interfere with the ability to perform routine maintenance required to keep the vehicle in service. In this regard, it is desirable to use a minimum number of conductors for passing coded information and to use commonly available cables or wires to interconnect the vehicle's master control panel and operator interface with a remotely located security module. This will help reduce the original cost of the system and the cost of servicing and replacing such wiring should that be necessary.
In light of the foregoing problems and desires, it is an object of the present invention to provide an anti-theft security system for an off-road vehicle that controls when an electrically-operated actuator on the vehicle may be operated, has few or none of the aforementioned shortcomings, and has virtually all of the aforementioned desirable attributes, including having an access code which can be readily changed by the vehicle operator or owner.
Other objects of the present invention include providing a vehicle security system that (1) is economical, reliable, and easy for an authorized user to disarm, while being difficult and time-consuming for a thief or other unauthorized user to defeat or bypass; (2) has a master control module with operator interface, preferably including a keypad and digital display, formed as part of the instrument cluster of the vehicle; (3) has a remotely located security module provided with a tamper-resistant housing enclosing decoding circuitry and an electrically-operated actuator such as a solenoid located therein; (4) employs two distinct access codes, one which the vehicle operator knows and enters to disarm the system, and another unknown to the vehicle operator and which is encoded in the signal sent between the master control module and the remote security module; (5) uses one or two conductors for sending a coded signal between the master module and the remote control module; (6) employs a sophisticated analog or serial digit encoding technique for encrypting the code in the signal between the master module and the remote module; and (7) provides electronic circuitry in the remote module for preventing damage that might be caused by accidental or deliberate over-voltage, short-circuiting, or transient electrical noise conditions, and for monitoring the internal status of the remote module for diagnostic purposes.